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Abstract

"Lanthanum Chromite, when used as the fuel cell interconnector material is exposed to extremely different oxygen activities on its two surfaces. In addition, it must also form coherent boundaries with the fuel electrode (anode) and air electrode (cathode) layers. In order to accomplish these functions the acceptor doped LaCrO3 must not only be chemically stable over large oxygen activity ranges, but also have good thermal expansion coefficient of match with both the anode and cathode. Therefore, the objective of this study is to investigate these requirements for Mg and Sr doped LaCrO3. The study was divided into three tasks, which are determinations of thermal expansion coefficient, dimensional stability, and lattice parameters of La.99CrO3 as the function of Mg and Sr-doped and oxygen activity.

Results show that the thermal expansion coefficient can be altered to match to that of the anode and cathode materials in the Solid Oxide Fuel Cell (SOFC) by the substitution of Sr on La lattices. The substitution of Mg on Cr lattices has little affect on the thermal expansion, so it by itself cannot being a match between SOFC components. Both Mg and Sr-substituted specimens expand when subjected to extremely reducing atmosphere ( < 10-16 atm.) at 1000 ˚C. This expansion in Sr-substituted compounds is about two to five times more than in Mg-substituted compounds. Under the most severe condition, the amount of expansion due to reduction is as much as due to thermal expansion for specimens heated from room to 350°C. Obviously, this expansion is sufficient to serve as the potential source of crack nucleation. Lattice parameters studies show that Mg substitution causes a slight expansion of the unit cell without causing a phase changes. The addition of Sr decreased the unit cell parameters and shifted the orthorhombic-rhombohedral phase transformation to lower temperature. No systematic changes in the lattice parameters were observed as the oxygen activity was varied"--Abstract, page ii.